The present invention relates to a rear projection screen used as a screen in a projection television system or the like.
There have been devised and demonstrated various types of rear projection screens. Recently the rear projection screens are used with the projection color television systems. That is, three primary color images, i.e. red, green and blue color images are projected on a screen and combined to form a color image, On the other hand, in the cases of color slide projectors and color motion picture projectors, a colored image is projected on a screen. Thus the former type rear projection screens have many problems to be left unsolved as compared with the latter type rear projection screens.
In the case of a projection system in which a plurality of different color images are projected on the rear side of a screen by different color projectors spaced apart from each other by a small distance. For instance, when a plurality of different color images are projected on the lens surface of a plano-lenticular lens, good color balance can be attained at the center portion, but the desired color balance cannot be obtained at the portions adjacent to the edge of the lens surface because of the difference in distribution of the intensity of the different color images.
In the case of color slide projectors and color motion picture projectors, luminance of the projected image can be considerably improved if the problem of cooling the projectors is overcome. In the case of the projection color television systems, when the electron beams scan a phosphor-dot screen, each phosphor dot produces red, green or blue light so that a considerably bright color image can be displayed on the screen. However, it is difficult to improve both luminance or brightness of the projected image and the lifetime. Moreover, the light emanating from a projection color television system must be efficiently converged to a viewing field.
In the case of the rear projection screen, the light beams emitted from a projector will not be interferred by a viewer so that a rear projection screen may be located at any convenient place in a relatively narrow room. Moreover, it has a further advantage that the rear projection screens can be used in relatively bright rooms. However, when ambient light is reflected by a screen or when a viewer or an object is reflected by a screen, the contrast of the projected image is lowered and consequently the visibility is degraded to some extent.
There has been proposed to use a combination of a Fresnel lens and a lenticular lens or a combination of a plurality of lenticular lenses as a rear projection screen. But when more than two lenses are used, diffusion planes are increased so that the resolution is reduced. Furthermore it requires a complicated and difficult process for cementing two lenses.